An electrical-dynamic position or correlated physical quantity transducer, which may be used as a pressure switch in a household appliance and which comprises a rigid casing accommodating within a deformable membrane sensitive to hydraulic pressure is known from Italian patent application n. 2002A000245; a first element consisting of a ferromagnetic core is engaged to the membrane so as to be mobile in a predetermined direction; and a second element consisting of an electrical winding forming an inductor, fixed to the casing, is operatively coupled with the first element to provide a signal variable according to the relative position of the first element with respect to the second.
For example, a relative motion of the core with respect to the inductor along the winding axis produces a variation of resonance frequency of the inductor, which may be detected and processed by a specific electronic circuit carried by the transducer casing, for example to provide a signal proportional to the differential hydraulic pressure exerted in use on the membrane, which, in the case of a washing machine or dryer, is subject on one side to atmospheric pressure and on the opposite side to a hydraulic pressure determined by the level of water present in the tank of the household appliance.
According to the contents of the aforesaid Italian patent application, the transducers of the described type require initial calibration of their transduction feature. Such calibration may be performed by mechanical means, as for example described in DE4444167 B4, or by means of an additional electronic circuit including a non-volatile memory unit for a series of corrective values to be applied to the values processed by the transducer, possibly provided with microprocessor.
However, the known mechanical calibration systems are large in size, present low reliability, are complex to make and assemble and are relatively difficult to use; and the electronic calibration system proposed by the aforesaid Italian patent application is costly and specialised personnel is required for correct use.